The reduction of the size and weight of the telephone, and thus in Particular the size and Weight of the batteries which serve as the source of power, without, however, shortening the time that the telephone can be used without having to recharge the battery, has Presented a continuous challenge in developing the usability of radio telephones. The time that a telephone with batteries of the same size can be used before it needs to be recharged can be lengthened if the consumption of current is reduced. For this purpose, numerous circuits have been developed by means of which, for example, the efficiency of the source of current has been improved and/or the consumption of current by the other circuits in the telephone have been somewhat reduced.
In general, the circuits referred to above are placed in a current-saving state when in an idle state, for example the operation of the microprocessor can be stopped. The circuits are reactivated by a suitable external control signal. Such a signal may be, for example, a receive or interrupt signal coming from a signalling circuit. With this procedure, however, an optimal saving of current is not achieved, since in general a circuit in a current-saving state will still receive a clock signal regardless of the internal state of the circuit. The clock signal is normally a high-frequency signal, for example of the order of megahertz and the output butter generating the clock signal consumes current.